Pregnant rats at various stages of gestation will be given estrogenic and progestogenic steroids and the fetal hearts will be examined by an automated chemical method which measures at least 20 phosphorylated intermediates. The records of control hearts and those from fetuses exposed to steroids will be compared to determine whether, and at what points, in the metabolic pathways differences may occur dur to the steroid exposure. Measurements can be obtained by the automated process on creatine phosphate, glucose-1-phosphate, alpha-glycerol-phosphate, dihydroxyacetone phosphate, mannose-6-phosphate, glyceraldehyde-6-phosphate, fructose-6-phosphate, glucose-6-phosphate, NAD, 2,3-diphosphoglyceric acid, UMP, AMP, fructose-1,6-diphosphate, UDP, IMP, ADP, GMP, GDP, NADH, ATP and GTP.